It is required to mold various kinds of stepped articles so as to prepare materials for sintering processes for the production of gears, pulleys or other machine parts. And, heretofore, molding machines having a principal portion such as shown in FIG. 8 have exclusively been used for the production of such various stepped articles.
In FIG. 8, pressure rams T1, T2, and T3 are positioned coaxially to core rod CR. Each one of said pressure rams is provided frictionally movably at least against an adjacent pressure ram or said core rod. And, power which has previously been charged in fixed mortar U is compressed by means of pressure rams T1, T2, and T3 and upper pressure rams which are not shown but are operated downwardly against pressure rams T1, T2, and T3, so that a stepped article can be molded. However, because such a molding machine is widely known and for the simplicity of drawings, said upper pressure ram and operating mechanism of the machine are omitted. Also, fluid pressure cylinders which are provided for the operation of pressure rams T1, T2, T3 are not shown.
And, as shown in FIG. 8, a mortar indicated at U is fixed to a mortar support TU which is fixed to a set of guide poles each indicated at G. Ram supports TS1, TS2, and TS3 which correspond to pressure rams T1, T2, and T3 respectively are positioned at a vertical distance apart from mortar support TU, ram supports TS1 and TS3 and core rod support CRS respectively. And, each one of said ram support or core rod support CRS is operated by a corresponding independent fluid pressure cylinder.
Further, in such a molding machine as shown, an upper pressure ram or upper pressure rams, not shown, is provided naturally so that powder charged in mortar U can be compressed for molding. In an exclusive machine for molding stepped articles of a fixed form having only a set of lower and upper pressure rams, vertical length of the machine can be out of consideration. But, in a machine for general use directed to the production of stepped articles having upper and lower principal faces of various shapes, a plural number of upper pressure rams and corresponding support structures are necessary to be provided. For this reason, a molding press heretofore known for the production of various stepped articles has a structure in which upper half portion of the machine has a structure having a feature substantially upside-down of that shown in FIG. 8.
Now, in a molding machine for general use, an amount of load to be impressed on each ram is different usually from one another according to shapes of the principal faces of articles to be molded. Accordingly, in a design of a molding machine, allowable amount of load for each ram support must be set at its possible maximum value that may be used in said molding machine.
On the other hand, because each one of said pressure rams or core rod CR, relates separately to actions for charging powder into the mortar, for temporary and real compression of powder, and for discharging molded articles. Accordingly, value of stroke length required for each pressure ram must be set at a value of the depth of said mortar and some surplus.
Moreover, an appropriate amount of room is required between said mortar support and an adjacent ram support, between ram support adjacent to each other, and between a ram support and said core rod support so that base portions and fixing bolts of said pressure rams and said core rod do not strike against said mortar support or ram support which are positioned above.
And, as each ram support is designed to have a thickness which corresponds to the maximum load for the corresponding ram as mentioned in the foregoing, an accumulation of thickness of said ram supports are added. So, the total length and the weight of the machine becomes very large. For example, for a machine having a mortar with depth for charge of 150 mm, and maximum value of load for each ram of 400 t/cm.sup.2, normally, the total length and the total weight including pressure rams of the machine mount up to 10 to 13 m, and 30 to 60 ton respectively. Accordingly, costs for equipment including a powerful fundamental construction and a workshop mount up to an enormous amount.
Further, as the pressure rams cannot be designed short, the work for exchanging die-sets or sets of pressure rams is complicated and troublesome, and an appropriate setting of die-sets cannot be effected by whom who is not a skilled person. In a molding business for the production of stepped articles, change in the object for molding occurs frequently. And, almost in every case, exchange of die-sets is required, and for the exchange of die-sets, principally a new design and manufacturing of a new die-set is required. In such cases, production cost for a precise die-set having large lengths is of course very large.
As a molding machine for general use for the production of stepped articles heretofore known has drawbacks as stated in the foregoing, this invention is directed to eliminate such drawbacks, and to provide a machine which is small in size and weight, and which is also small in costs for equipment, and to provide a machine which is convenient in operation, and accordingly has a high economic value.